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Petroleum Engines.

705

as shewn in Fig. 688. The pendulum may be adjusted to the
greatest nicety by raising or lowering ball n. The method or
opening the exhaust valve is seen in Fig. 686. A cam e on the
shaft Q lifts the lever T, pivoted at u, and, through rod v, the
'crocodile jaw' w; thus raising the valve against the springs a a.
w has a shifting fulcrum at x, giving a larger leverage at first, and
a quicker opening afterward.

Fig. 684 shews the indicator diagram obtained, which still
further illustrates the Otto cycle. One difference in the Simplex
working is noticeable; the mixture is over-compressed, that is,
a small return motion is made, after leaving the dead point,
before ignition occurs, and the force of the explosion only reaches
the crank when it is in a better position, viz., at 15 from dead
centre.

For the best economy, gas engines should work with 'poor
gas,' as produced by the Dowson plant in England, and the
Buire-Lencauchez in France: the latter is used in conjunction
with the Simplex Engine. Rich lighting gas is expensive for
large engines. (Seefjb. 911 and n$i.)

Petroleum or Oil Engines, like gas engines, are of the
internal combustion type. Petroleum occurs naturally in Russia
and America, but is also obtained as paraffin by shale distillation.
It is highly complex, consisting of several liquid hydrocarbons
having different boiling points: thus, when heated, giving off
first the lighter oils, then the burning and lubricating oils, and
lastly paraffin wax or vaseline, leaving a residuum. The light
oils, including benzoline and naphtha, are dangerous, flashing at or
below 73 F.; while the heavy or lighting oils, like kerosene, are
thoroughly safe, resisting the flame of a match, or even the
electric spark. But the heavy oils are difficult to prepare for
the motor, where they are to be intimately mixed with air to
form the charge: if vaporised at low temperature, a troublesome
residue is formed, while gasification at high temperature produces
also tar.

In 1838 Messrs. Priestman Bros, acquired the Eteve patents
(where spraying with air and evaporating in a hot chamber was
first proposed), and after considerable experiment produced the
first practically successful engine working with safe oil, doing for